Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting a frame in a wireless local area network (WLAN).
Related Art
In a wireless local area network (WLAN) system, distributed coordination function (DCF) may be employed as a method enabling a plurality of stations (STAs) to share a wireless medium. DCF is based on a carrier sensing multiple access with collision avoidance (CSMA/CA).
Generally, in operations under a DCF access environment, when a medium is not occupied (that is, idle) for a DCF interframe space (DIFS) interval or longer, an STA may transmit a medium access control (MAC) protocol data unit (MPDU) to be urgently transmitted. When the medium is determined to be occupied according to a carrier sensing mechanism, an STA may determine the size of a contention window (CW) using a random backoff algorithm and perform a backoff procedure. The STA may select a random value in the CW to perform the backoff procedure and determine backoff time based on the selected random value.
When a plurality of STAs attempts to access a medium, an STA having the shortest backoff time among the STAs is allowed to access the medium and the other STAs may suspend the remaining backoff times and wait until the STA having accessed the medium finishes transmission. When the STA having accessed the medium finishes frame transmission, the other STAs contend again with the remaining backoff times to acquire a transmission resource. As such, in the existing WLAN system, one STA occupies the entire transmission resource through one channel to transmit/receive a frame to/from an AP.
In the WLAN system, the STA may determine whether a medium is busy or idle on the basis of clear channel assessment (CCA). That is, before the STA transmits a frame, whether the medium is used by another STA may be decided on the basis of the CCA. Whether to use the medium may be decided on the basis of a CCA threshold. A physical layer of the STA may report information regarding a channel state known through the CCA (information regarding whether to use the medium) to a medium access control (MAC) layer of the STA.